The definition of STL has been changed to cater for boats that do not use a spinnaker but fly a large headsail from the end of the bowsprit. All ratings will therefore include an STL measurement even if not rated for spinnakers.

To simplify the Rule, a new definition Aft Rigging has been added: IRC will no longer distinguish between backstay(s), running backstays or checkstays.

New rule 19.6 has been added requiring declaration of materials over specific gravity of 8.0 (eg. lead) in some types of keel fin. This is to counter the trend of moving lead from the bulb into the fin.

Rule 2.6 has been updated to reflect actual practice.

The new ERS 2017-2020 now incorporate definitions that were previously included in the IRC Rule, so these have been removed or updated as appropriate.

A number of detail changes have been made throughout the text to correct typographical errors and inconsistencies in terminology.